I remember the time, many, many years ago, when the iOS simulators were actually extremely light, fast and efficient. They could simulate in real-time, full 60fps, even on slower Macs.

With every new version of Xcode, the simulators have become increasing slower. By this point they have become so slow that they are almost unusable. The Xcode 9 simulators were already really slow (running at about 10 fps on this iMac), but now with Xcode 10 they have become even slower. In fact, it's worse now because with Xcode 9 they were slow, but at least the framerate was quite steady and consistent. With Xcode 10 there framerate will fluctuate, between about 10 fps and something like 2 fps, at random intervals, making it almost unusuable.

This is even worse than ever before because now the simulator hogs 100% of CPU time, making everything in the operating system lag while the simulator is running. I can't do anything else at the same time.

Luckily this is probably the last iOS project I ever have to do with Xcode.

Thanks for the tip Warp. Rolled back to 11.4 for maybe 50% improvement. Still a bit hesitant and jerky. May need to roll back further until12.1 or 2 comes along. At 2GB per simulator its annoying, as they were all downloaded before and existing on my machine before 12.0 update.

Other co-existing suspects.

* had a PUP (Mac Mechanic) on system - now gone I think?

* there has been a Java update recently?

* my mouse is intermittantly disconnecting. Reonnects on demand, but a new and bothersome symptom for a system which should have matured with robustness & reliability & some certainty after this many years. Apple's appetite for unwarranted change & deprecation irks me.

Simulators have become ridiculously slow. Timing any kind of transition or animation is impossible. I have tried every solution so far from changing FramebufferRendererHint to reinstalling simulators. I am about ready to go back to Microsoft world. Yesterday (xcode 9.xx) I was productive, today (Xcode 10) I cannot even get any work done. Absolutely insane. This is not a beta version either, This is the production version.

Things seem to be in working order now and I don't have to result to using Xcode 9.2 (although I'll continue to use it on my other machine running High Sierra should I encounter any issues with this 10.1).

For the time being, I will continue to document any issues should I encounter any but I am definitely pleased with the patch Apple provided for macOS Mojave 10.14.1 Beta which seems to work marvelously in conjunction with Xcode 10.1.

We have several mid-2011 27" iMac (3.4 GHz Intel Core i7) running High Sierra 10.13.6 with Xcode 10. All exhibit the same slow-down when trying to use the Simulator. If the Simulator is left running in the background the entire OS will eventually come to a halt until the Simulator is forcibly stopped.

Seems to be slightly less of a problem on some newer Macs (e.g. mid-2017 MacBook Pro; mid-2013 27" iMac).

Either way, it's making development for our team extemely difficult.

Will try running ‘xcrun simctl diagnose’ and ‘sudo sysdiagnose -q’ when in this slowed state and attach the resulting tarballs to a bug report to see if that helps with any form of recognition / diagnosis.

FYI - this workaround might help some of you in the meantime, but we've noticed that if you run the iPhone 5S / SE - 7, the slow-down is not as prevalent. Any newer devices are more or less unusable from the moment they open.

As a trial I removed assigning of images to UIButton from start-up and processed it after start-up separately, also on main-thread. Total 47 setImage: or setBackgroundImage: take 1 (iPhone SE) or even 2 seconds (iPhone 8 Plus) on iOS 12 simulator !!

Is there any official word from Apple about this or are they just attempting to get developers to fork out for the actual devices and or newer more powerfull and expensive devices to work from as with so many threads on this issue over so many different versions and years without it being addressed it sort of feels and looks like its intentional.

When using macos 10.13.6 and xcode 10 on mac pro 5.1, starting the simulator it's getting so slow and lagging, that you cannot work. Also entire system is getting slow. Rolling back to xcode 9 woun't help. Only time machine helps. Rolled back to 10.13.4 and xcode 9. Tried xcode 10.1 beta, the problem still exists. Can't update this mac to Mohave because of Apple requires only cards with metall support((

I had the same problem with very slow simulator behavior on my Mac Pro 5.1 with XCode 10 (12 cores, 128GB RAM); simulator performance is fine on my Macbook Pro using XCode 10

In order to upgrade to Mojave I swapped to a metal-capabile GPU (supplied a few years ago by a well-known flasher based in Hollywood) and that solved the problem (well, either the graphics card or the Mojave upgrade did)

If those technical specs are not applicable to you, kindly disregard the following next steps I'll be presenting to squeeze more speed, optimal performance and efficiency out of your iOS Simulators running iOS 12 and above.

The reason why I specify these specs is because I've been downloading every single beta release since Mojave first came out and have been closely following each sequential release as a means of tracking which bugs have been addressed or fixed and if any beta release actually provides more optimal performance to my machine.

In this case, since we're discussing Xcode 10, let's begin:

First order of business: get rid of Dark Mode altogether, you don't need it as much as you think you do. It's gimmicky and actually slows down your performance on Xcode in every shape and form. Notice that weird lag when you're trying to get your iOS Simulator going while simultaneouly browsing Chrome? That has definitely been attributed to Dark Mode in my case and I have seen a substancial difference in performance when running my apps on the Simulator.

Turn off your device bezels by doing the following: Simulator > Window > Show Device Bezels (uncheck it if it checked by default).

Since applying the following changes to my Simulator preferences, indexing takes less effort out of Xcode, launching the Simulator itself is almost instananeous and app installation happens in seconds. While it's not the record speed that I'm used to from Xcode 7.3.1 or even Xcode 9.2, it makes version Xcode 10 a lot more usable than before I implemented some changes on machine settings.

Again, I haven't tested any of these changes on Xcode 10 GM so this could potentially help just about anyone even if they're not running macOS Mojave beta or even Xcode 10 beta versions. I simply wanted to emphasize that my machine could be different than yours in the aspect that I'm running beta software so implement these relatively harmless changes at your own discretion.

I have the same issue... and I've been having it since Xcode 9 actually... I quickly decided to try the 10 beta hoping it was fixed.

But nope - I have all the latest updates to Mojave and Xcode and the Simulator most of the time is unusanle. It takes multiple clicks (like 10-20) to perform an action like touch, and then it takes a few seconds to do the action. I don't know how to fix it - reminds me of Windows.

Is the common factor "slightly older MacBook Pro"? That's what I've got, and the simulators are totally unusable. They are, oddly, somewhat better if Slow Animations are turned on, though then of course the simulation is not so realistic and everything takes longer.

I realize this is a late response, but I ran into this issue today and after searching on stackoverflow, I found that I had inadvertently pressed command+T, which triggers the "Slow Animations" (under the Debug menu in simulator). Pressing command+T again (or unselecting it in the menu) fixed the problem!

(I have option+command+T set to be a keyboard shortcut for the simulator's Hardware->Touch ID->Matching Touch command, I missed the option key and just hit the command+T accidentally, it didn't log in to my app, so pressed option+command+T again, then logged in and everything was sooooo.... slooooowwwwwww....... I thought some of the new code I added to the app caused a major problem, but removing it didn't help—it didn't dawn on me that I had hit command+T accidentally prior to this happening, then I found the stackoverflow answer, unchecked "Slow Animations" from the Debug menu, and all is back to normal!) Hope it's this simple fix for others who run into this issue.

The core issue here is that older versions of the simulator use the CPU for rendering. iOS 13 running on Catalina will utilize the GPU through Metal. You should have a much better experience with this year's releases.

I would like to share my knowledge with simulator performance issue. I have hybrid HTML5 + JavaScript app (web/android/iOS) and for android/iOS mobile apps I use web-view. I detected that some part of my app is extremely slow in Xcode simulator. It is part with Date object manipulations. When I run e.g. this simple JavaScript code

in cycle with e.g. 1000 iterations it runs fast (several tens milliseconds e.g. 30 ms) in any browser any device any platform including very old iOS device e.g. iPhone 5C and several years old iPad 2, BUT IN SIMULATOR IT TAKES 6000 ms (yes, 6 seconds!). So simulator is 200 times slower! Terrible! Jsfiddle demo here: https://jsfiddle.net/kjms16cw/ I see in Xcode console error: "[IPC] Connection::waitForSyncReply: Timed-out while waiting for reply". Interesting is that Xcode during that 6 seconds show app CPU usage 0% but in host device (MacBook Pro) monitor I see that CPU increased from about 5% before to 50% during test. Dear Apple can you explain please that low simulator performance? So Im not possible to test my app in simulator at all... we also need simulator for testing but also for creating screenshots for several resolutions required before app publishing in app store. My app is for public transport and we need to do lot of date calculations each second (several hundreds) which usually takes 10 ms but in simulator several seconds and interval each second makes app totally unresponsive and unusable in simulator.

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